1. Field of the Invention
The present invention relates to a production method of a dielectric ceramic composition used as a dielectric layer of, for example, a multiplayer ceramic capacitor, a dielectric ceramic composition obtained by the production method, and an electronic device using the dielectric ceramic composition as a dielectric layer.
2. Description of the Related Art
A multilayer ceramic capacitor as an example of electronic devices is produced, for example, by alternately stacking ceramic green sheets made by a predetermined dielectric ceramic composition and internal electrode layers of a predetermined pattern and unifying the result, and cofiring a thus obtained green chip. It is necessary that a material which does not react with a ceramic dielectric is selected for the internal electrode layer of the multilayer ceramic capacitor so as to be unified with the ceramic dielectric by firing. Therefore, costly precious metals, such as platinum and palladium, had to be used as the material composing the internal electrode layer.
However, in recent years, a dielectric ceramic composition wherein an inexpensive base metal, such as nickel and copper, can be used has been developed and a major cost reduction has been realized.
Also in recent years, a demand for a more compact electronic device has become high along with an electronic circuit becoming high-density, and a multilayer ceramic capacitor has been rapidly become more compact and higher in capacity. To respond thereto, it has been essential to make a thickness of one dielectric layer thinner in a multilayer ceramic capacitor. However, when a dielectric layer is made thinner, there arises a disadvantage that a short-circuiting defective is frequently caused. As one method to solve the disadvantage, there is a method of making dielectric particles composing the dielectric layer finer. However, in terms of improving characteristics of the multilayer ceramic capacitor, it is necessary not only to make the dielectric particles simply finer, but to maintain preferable electric characteristics also when made to be finer.
In the Japanese Unexamined Patent Publication No. 2001-316176, fine dielectric particle (dielectric ceramic particle) having preferable electric characteristics is obtained by using particles having fine particle diameter as barium titanate base ingredient powder as a main component ingredient, and limiting the maximum particle diameter and the particle distribution. It is disclosed that the DC bias characteristic of the multilayer ceramic capacitor can be made preferable by using the dielectric particle as a dielectric layer of the multilayer ceramic capacitor.
The ceramic multilayer ceramic capacitor described in the above article, particularly the multilayer ceramic capacitor disclosed in the examples is added an extremely large amount of subcomponents, such as Mn and Mg, in the dielectric particles composing the dielectric layer. By adding a large amount of Mn and Mg, etc. as such, dielectric particles can be made finer, but a decline of electric characteristics, for example, a decline of insulation resistance, etc. is caused at the same time. In the multilayer ceramic capacitor in the article, there is no problem caused since a thickness of the dielectric layer is made to be 30 μm, but when the dielectric layer is made thinner to, for example, 5 μm or less, an increase of the insulation defective occurrence rate caused by a decline of insulation resistance as above and deterioration of high temperature load lifetime are inevitable.